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Ing. Klára Vokáč Machalická, Ph.D.

2024, Buildings, 14 (2), ISSN 2075-5309

Kevlar fibers are widely used for industrial and military purposes due to their remarkable mechanical properties, such as their high tenacity and high strength-to-weight ratio. In this study, two-layered Kevlar composite specimens were impregnated with 10 wt.% poly (vinyl butyral)/ethanol solution which contained TiO2 nanoparticles as reinforcement. The concentrations of the nanoparticles were 1 wt.% or 2 wt.% with respect to the poly (vinyl butyral), PVB. The single-axial tensile test and three-point bending test of the Kevlar/PVB composites have been performed according to the ASTM D 3039 and ASTM D 790-03 standards, respectively. The tensile and bending properties of the dry and wet Kevlar/PVB composite specimens after a 56-day immersion are examined in this work. Upon the addition of the 2 wt.% TiO2 nanoparticles, the tensile strength and modulus of the dry specimens without reinforcement were increased by 39.8% and 24.3%, respectively. All the submerged specimens’ tensile and flexural property values were lower than those of the dry specimens. After comparing the wet composite specimens to their dry counterparts, the percentage decrease in tensile strength was approximately 20%. The wet Kevlar/PVB specimens with no TiO2 reinforcement showed the greatest reduction in bending strength, 61.4% less than for the dry Kevlar/PVB specimens, due to the degradation of the PVB matrix. In addition, a numerical simulation of the three-point bending test was carried out in Abaqus.

2024, MecaNano 2nd General Meeting - Book of Abstracts, Vídeň, Technische Universität Wien)

The Kevlar fabric composites are widely applied for body armor and vehicle armor structures. In this study, the specimens were produced of the Kevlar fabrics impregnated with 10 wt.% poly (vinyl butyral)/ethanol solution which contained the ZnO nanoparticles in different concentrations (1 wt.% or 2 wt.% in relation to poly (vinyl butyral), PVB). The two-layered Kevlar/PVB composite samples were fabricated by hot compression. In accordance with the ISO 62 standard, the square Kevlar/PVB composite specimens were immersed for the water uptake measurements. The tensile and flexural properties of the Kevlar/PVB specimens were examined in compliance with the ASTM D 3039 and ASTM D 790-03 standards, respectively. The specimens that had been submerged in distilled water at 40 ◦C for eight weeks were compared to the dry specimens in terms of their tensile and bending characteristics. The addition of ZnO nanoparticles significantly improved the tensile strength and tensile modulus of the dry Kevlar/PVB specimens. In contrast to the tensile test results, the dry specimens with no nanoparticles exhibited the superior flexural qualities (strength and modulus) because of the better bonding between their two impregnated fabric layers. When compared to their dry counterparts, the tensile and bending properties of every immersed Kevlar/PVB composite specimen showed some lower values.

2024, Buildings, 14 (6), ISSN 2075-5309

Rooftop solar modules are usually held in place by racks or frames that are mechanically attached to a roof structure and/or by heavyweight, ballasted footing mounts. These mounts ensure that the panel system remains in position against wind load. However, mechanical connectors create penetrations into the water-resistant layer of the roof, whereas ballasted footing mounts cause a significant additional load on the load-bearing structure of roof. For these reasons, adhesive connection seems to be a beneficial solution. Acrylic adhesive tapes, marked as VHB, may provide sufficient strength, and they have no need for mechanical fasteners or ballast. Acrylic adhesive tapes also provide a comfortable, fast, and efficient bonding process with no curing compared to liquid adhesives. On the other hand, resistance to water at load-bearing joints has not been sufficiently studied yet and could be critical for connections exposed to the outdoor environment. The present study aims at the determination of water resistance and durability of the VHBTM tapes from the GPH series, which are typically used to bond a variety of substrates including many metals. The mechanical properties and failure modes are compared for the specimens before and after a 21-day immersion in water. A significant reduction in strength was observed, depending on the substrate material. The study of chemical changes in the acrylic tape and in its leachate through infrared spectroscopy (FT-IR), X-ray fluorescence, and X-ray diffraction analyses clarified the reduction in mechanical properties. The selected VHB tape demonstrated strong resistance to the effects of water. However, the overall strength of the joint after immersion was significantly impacted by the decrease in adhesion to a specific substrate.

2023, Modern Building Materials, Structures and Techniques, Springer, Cham), p. 268-277), ISBN 978-3-031-44602-3, ISSN 2366-2557

The Kevlar fabric composites have a wide range of applications in the body armor and lightweight vehicle-armor structures. Nanoparticles are one of the most common nanofillers for these structures. In this research, the testing specimens have been made from the Kevlar fabrics impregnated with the poly (vinyl butyral)/ethanol solution which had been reinforced with the ZnO nanoparticles. The two-layered composite samples have been fabricated by means of hot compression. The immersion of the square Kevlar/PVB specimens for the water uptake measurements has been performed according to the ISO 62 standard. The specimens have been immersed in a water bath filled with the distilled water (40 ℃) in the period of 8 weeks. The Kevlar/PVB specimens have been tested in accordance with the ASTM D 3039 standard for the tensile properties and the ASTM D 790–03 standard for the flexural properties. The tensile and bending characteristics of the dry specimens have been compared with the ones that had undergone the water immersion.

2023, ICFC9 9th International Conference on Fatigue of Composites - Scientific Program and Book of Abstracts, Padova, University of Padova), p. 48-48)

In this research, the testing specimens were made from the Kevlar fabrics impregnated with 10 wt.% poly (vinyl butyral)/ethanol solution but with the addition of the TiO2 nanoparticles. The tensile and bending properties of the dry specimens were compared with the ones that had been immersed in a water bath filled with distilled water (40°C) in the period of 8 weeks. The PVB/fabric weight ratio for the impregnation of the woven Kevlar fabric was 20 wt.%. The Kevlar/PVB fabric composites were reinforced with the TiO2 nanoparticles in different concentrations (1 wt.% or 2 wt.% of reinforcement regarding poly (vinyl butyral), PVB). The two layers of composite fabrics were hot-pressed by using the digital press at a temperature of 170 °C for 30 minutes. The immersion of the square Kevlar/PVB composite specimens for the water weight gain measurements was performed according to the ISO 62 standard. The Kevlar/PVB specimens were tested in accordance with the ASTM D 3039 standard for the tensile properties and ASTM D 790-03 standard for the flexural properties. During the tensile and the flexural test, the complete fracture of the specimens did not occur. The addition of 2 wt.% TiO2 nanoparticles produced 39.8% and 24.3% improvement in the tensile strength and tensile modulus, respectively, compared to the dry Kevlar/PVB specimens without reinforcement. The tensile properties of all the immersed Kevlar/PVB composite specimens had decreased values compared to the ones of their dry specimens. Unlike the tensile test results, the best flexural properties (strength and modulus) were achieved with the dry specimens with no particles due to the better bonding between their two impregnated fabric layers since the presence of TiO2 nanoparticles reduced the shear connection between the layers. However, there was not such a decline in the properties of the wet specimens with nanoparticles which even made some improvement in the bending strength compared to the wet Kevlar/PVB specimens.

2022, Composite Interfaces, 29 (12), p. 1309-1324), ISSN 1568-5543

Carbon fiber reinforced polymer (CFRP) composites have many applications in civil engineering, aircraft industry and in many other areas. They are lightweight composite materials with outstanding mechanical properties. In this study, the testing specimens were made from the carbon fabrics impregnated with epoxy resin which had been reinforced with the silicon carbide (SiC) microparticles or SiC microfibers. The four-layered composite samples were fabricated by means of hot compression and curing of epoxy resin. The thermal, tensile and impact properties of the untreated specimens were compared with the ones that underwent the water absorption in duration of 72 hours, followed by desorption. The treated specimens containing the SiC particles and SiC microfibers demonstrated 3.4% and 8.8% of the reduction in the tensile energy absorption, correspondingly, compared to their untreated counterparts. Opposed to this trend of results, the tensile energy absorption value of the treated carbon/epoxy specimens, experienced an increase of 84.4% compared to the dry carbon/epoxy specimens. The additional test results showed that the water treated carbon/epoxy composites went into a certain decline in their thermal, tensile and impact properties. The obtained results provide some significant pieces of information for the future practical use of the presented composites.

2022, The Journal of Adhesion, 98 (14), p. 2133-2209), ISSN 1545-5823

The development of new adhesives has allowed to expand the application of bonding into the most diverse industrial fields. This review article presents the commonly used experimental methods for the investigation of mechanical performance of adhesively bonded joints in the aerospace, wind energy, automotive and civil engineering sectors. In these sectors, due to their excellent intrinsic properties, composite materials are often used along with conventional materials such as steel, concrete and aluminium. In this context, and due to the limitations that the traditional joining techniques present, adhesive joints are an excellent alternative. However, standardized experimental procedures are not always applicable for testing representative adhesive joints in these industries. Lack of relevant regulations across the different fields is often overcome by the academia and companies’ own regulations and standards. Additional costs are thus mitigated to the industrial sectors in relation with the certification process which effectively can deprive even the biggest companies from promoting adhesive bonding. To ensure continuous growth of the adhesive bonding field the new international standards, focusing on actual adhesive joints’ performance rather than on specific application of adhesive joints are necessary.

2022, CertBond COST Action CA18120 – Training School 2 – Book of Abstracts, TECHNISCHE UNIVERSITEIT DELFT), p. 40-40)

Carbon fiber reinforced polymer (CFRP) composites are extensively employed in aircraft industry, and in other areas where outstanding mechanical performance is a requirement. In this study, the composite samples were made from the carbon fabrics impregnated with epoxy resin reinforced with the silicon carbide (SiC) microparticles or microfibers. The thermal, tensile and impact properties of the untreated specimens were compared with the ones that underwent the water absorption in duration of 72 h (immersion or high humidity) followed by desorption. The glass transition temperatures (Tg) of the specimens were determined using the differential scanning calorimeter (DSC) device. The carbon/epoxy specimens were tested in accordance with the ASTM D5942 standard for their impact properties and ASTM D3039 standard for the tensile properties of the composite materials with the polymer matrix. The dry carbon/epoxy specimens with the SiC microfibers or SiC particles showed a large increase in the tensile strength and tensile energy absorption (TEA), respectively, in comparison with the dry carbon/epoxy specimens while the specimens with the SiC particles had the highest value of the impact toughness. The carbon/epoxy specimens with the SiC reinforcement, which were exposed to 70% humidity or water immersed, saw the decline in Tg. The tensile strength and TEA of the water immersed carbon/epoxy specimens with the SiC reinforcement had the values decreased in comparison with the ones of their dry specimens. Contrary to this trend of results, the tensile properties values achieved a significant increase in the immersed carbon/epoxy specimens (with no reinforcement), in comparison with the dry ones. The decrease of the elastic modulus was determined in all the specimens after water immersion followed by desorption. The impact toughness values of all the specimens decreased after exposing them to the elevated humidity as well as to water immersion, compared to the values in their untreated counterparts.

2021, Current Applied Physics, 26, p. 16-23), ISSN 1567-1739

Para-aramid fibers (Kolon) are high performance polymeric fibres characterized by their high tenacity and impact resistance. They are used for the soft body armor structures in ballistics. In this study, the testing specimens were made from multilayered Kolon fabrics impregnated with epoxy resin where silicon carbide (SiC) microparticles or SiC nanofibers were added as reinforcement. The laminated composite samples were fabricated by hot compression and curing of epoxy resin. The tensile and impact strengths of the untreated specimens were compared with the ones that underwent water absorption in duration of 72h (immersion or humidity) followed by desorption. The immersion of the specimens in water and exposure to high humidity (70%) were performed according to the ISO 62 standard while the tensile test was carried out in accordance with the ASTM D 3039 standard. In the end, the tensile test simulation of the laminated composite by using software Abaqus® was accomplished.

2021, 15th International conference on materials chemistry (MC15), Cambridge, Royal Society of Chemistry)

The para-aramid fibres (Kevlar, Twaron, Kolon) are high performance polymeric fibres characterized by their high tenacity, strength to weight ratio and impact resistance. They are used for the soft body armour structures in ballistics and for the manufacture of parts in aerospace and automotive industry. In this study, the specimens were made from the two-layered Kolon fabrics impregnated with epoxy resin where some silicon carbide (SiC) microparticles or SiC nanofibres were added as reinforcement. These composite specimens were fabricated by hot compression and curing of epoxy resin. Despite their good mechanical strength it is a well-known fact that the mechanical properties of epoxy resins are affected by moisture absorption. The tensile and impact properties of the untreated specimens were compared with the ones that underwent water absorption in the duration of 72h (immersion or humidity) followed by desorption. The immersion of the specimens in water and the exposure to high humidity (70%) were completed in accordance with the ISO 62 standard while the tensile test was performed according to the ASTM D 3039 standard. Furthermore, the tensile test simulation of the Kolon/epoxy composite by using software Abaqus® was accomplished. For the determination of the absorbed impact energy and the impact toughness of the composite specimens, an impact test was performed by using the Charpy impact pendulum in accordance with the ASTM D5942 standard.

2021, Materiály pro stavbu (4), ISSN 1213-0311

Sklo se díky svým estetickým vlastnostem, nejen transparentnosti, ale také díky svému hladkému, lesklému, a především odrazivému povrchu, stalo důležitým materiálem moderní architektury.

2020, International Journal of Adhesion and Adhesives, 97, ISSN 0143-7496

For civil engineering applications of adhesive bonds, the service lifetime and environmental ageing is a fundamental question for safe design. The paper compares the effects of three different ageing procedures (immersion in warm water according to ETAG 002, neutral salt spray test according to ISO 9142, Procedure E4, and extended cataplasm test based on ISO 9142, Procedure E2) among each other on adhesives which are applicable in the civil engineering field. The research covers two different adhesives (two-part acrylate and silane terminated polymer, STP) applied in double lap shear joints composed of aluminium and Zn-electroplated steel substrates. Aluminium was used in two types of alloy and also as anodized aluminium due to its wide use in building facades. All mechanical test results were put in context with chemical analysis results to better understand the changes in the adhesive joint after environmental ageing.

2020, Engineering Structures, 223, ISSN 0141-0296

There are many examples of glass load bearing structures used in a contemporary architecture, such as panes, balustrades, and even stairs. For safety reasons, these structural elements are made of laminated glass which is a composition of glass plies bonded with polymeric interlayer. The distribution of stress in a perpendicularly loaded laminated glass panel depends on the shear stiffness of the used interlayer. There are various interlayers for laminated glass applications available on the market with wide variety of shear stiffness. To correctly evaluate the shear coupling provided by the interlayer, great research efforts have been made followed by appropriate national Standards and Codes for laminated glass in bending in recent years. Polymeric interlayers are viscoelastic materials and their stiffness is time and temperature dependent, which makes the reliable design of laminated glass panel in bending rather complicated. This paper is focused on experimental investigation of six polymeric interlayers (Trosifol® BG R20; Trosifol® Extra Strong; Evalam® 80/120; Evasafe®; SentryGlas® 5000; Krystalflex® PE399) loaded in displacement-controlled shear test in various temperatures and loading rates. The experiments showed nonlinear stress–strain dependence and confirmed the viscoelastic behaviour of presented interlayers. In addition, the values of their initial shear stiffness are listed and failure modes of testing specimens are presented. Results obtained in this study can be used for the estimation of the rate of glass plies interaction in short-term loaded laminated glass structures. All experiments were performed in Klokner Institute CTU.

2020, Challenging Glass 7 - Conference on Architectural and Structural Applications of Glass, Delft, Delft University of Technology (TU Delft)), ISBN 978-94-6366-296-3

The paper compares the experimental data from displacement-controlled four-point bending tests in various loading rates and from four point bending long-term creep experiments of double laminated glass panels with PVB interlayer Trosifol®BG R20 to the numerical analysis. The interlayer was modelled as a viscoelastic material by two discrete Maxwell models. Prony parameters of the first Maxwell model were based on DMTA results performed on small scale specimens in single lap shear mode and Prony parameters of the second Maxwell model were based on combined DMTA results performed on small scale specimens in single lap shear mode and torsion mode.

2020, Acta Materialia Turcica, 4, p. 30-36), ISSN 2630-5909

The paper reports on an experimental analysis focused on determining the mechanical characteristics of two types of acrylate adhesives applied in a double lap connection loaded by shear. The study comprises two basic substrate materials often used in façades both for cladding and for substructure – aluminium and galvanised steel. Both materials are applied with a smooth and mechanically roughened surface to compare adhesion in relation to the laboriousness of surface preparation. Except for blank aluminium, anodised aluminium was also used. Material and surface treatment has a great influence not only on adhesion and hence strength of the joint but also on failure mode, behaviour and safety of a particular joint. Moreover, every necessary surface treatment creates higher labour intensity, higher time consumption and thus increased costs. Our results showed different behaviour of both chosen acrylate adhesives in spite of their similar chemical bases. The first acrylate, two-part structural methacrylate, showed shear strength from 12 to 17 MPa in dependence on substrate material with shear strain between 0.6 and 1.2. The best adhesion was observed at roughened galvanised steel substrates. The second acrylate adhesive, two-part structural adhesive based on acrylic double performance polymer technology (ADP), proved shear strength from 8 to 9 MPa for aluminium substrates and less than 6 MPa for galvanised steel substrates. ADP adhesive also showed higher shear strain values (approx. 2.8). The experimental study proved that a choice of the adhesive has a great influence on the mechanical properties of adhesively bonded joint as well as on adhesion to a particular substrate even in the case of a similar chemical base of adhesives.

2020, 5th International Conference on New Advances in Civil Engineering, Melville, NY, AIP Publishing, APL, the American Institute of Physics), ISSN 1757-8981

Laminated glass is getting used more extensively in a current architecture due to its transparency, aesthetic impression, and post-breakage behaviour. Examples of such structures are balustrades, stairs, or facade panels. These are usually loaded in bending. Polymeric interlayer embedded between glass plies has no flexural stiffness, but it can itself transfer shear stress. The rate of this transfer depends on the shear stiffness of interlayer which is time and temperature dependent parameter. Producers of interlayers often do not specify this quantity thus engineers rather neglect the shear interaction of glass plies in perpendicularly loaded laminated glass panels. This paper provides the values of shear stiffness modulus of common interlayer EVASAFE® by BridgestoneTM in time and temperature domain. This shear stiffness is expressed through Maxwell model whose parameters are based on the series of Dynamic mechanical thermal analysis (DMTA) performed on single lap small-scale specimens in Klokner institute CTU in Prague. Results show that shear stiffness of this interlayer is able to provide significant shear coupling of glass plies in broad temperature range of short-term perpendicularly loaded laminated glass structures.

2020, Acta Materialia Turcica, 4, p. 37-42), ISSN 2630-5909

In contemporary architecture, laminated glass panes are widely used for structural elements loaded perpendicularly to its surface such as floors, roofing, facades etc. It is sought-after for its transparency and smooth reflective surface. In this case, it is advisable to consider the interaction of the individual glass panes in the cross-section. A conservative approach, that does not take into account the shear interaction of glass panes, is uneconomical. Various commercial products based on PVB (polyvinyl butyral), EVA (ethylene vinyl acetate), ionomer, or thermoplastic polyurethane (TPU) are used. Stiffness of polymers depends on temperature and duration of a load. Interlayers exhibit the viscoelastic properties and temperature dependency is usually described by the generalized Maxwell model and WLF model (Williams-Landel-Ferry). Parameters of these models are most effectively determined by Dynamic Mechanical Thermal Analysis (DMTA), where the material is cyclically loaded at different frequencies and temperatures. Two types of PVB interlayers (Trosifol® Extra Strong and Trosifol® BG-R-20) were investigated using DMTA in the research carried out at Klokner Institute, CTU in Prague. In addition, experimental quasi-static loading tests were performed in shear at various loading rates and temperatures. The testing arrangement was as single lap shear test in both cases. The experimental stress-strain diagrams from static tests were compared with the theoretical diagrams derived from material parameters based on DMTA testing. Although both materials are PVB-based, shear stiffness and temperature dependence are considerably different due to additives added to the PVB feedstock. These differences in material behavior are important because the actual material properties have to be taken into account in the design of laminated glass structure.

2019, MODERN BUILDING MATERIALS, STRUCTURES AND TECHNIQUES MBMST 2019, VGTU Press), p. 336-343), ISBN 978-609-476-197-3, ISSN 2029-9915

Various examples of glass load bearing structures such as beams, columns, panes, or even stairs are used in a current architecture. For safety reasons, these members are mostly made of laminated glass. Polymeric interlayers are used for glass plates bonding and their shear stiffness, as a time-temperature dependent parameter, significantly influences the response of the entire perpendicularly loaded laminated glass pane. This paper compares the results of perpendicularly loaded double laminated glass panes at various boundary conditions, calculated by analytical methods and by the draft of prEN 16612 to the numerical simulation.

2019, MODERN BUILDING MATERIALS, STRUCTURES AND TECHNIQUES MBMST 2019, VGTU Press), p. 533-538), ISBN 978-609-476-197-3, ISSN 2029-9915

Adhesive bonding is commonly used in the automotive and aerospace industry, where it has proved its advantages. Nowadays, the bonded joints are starting increasingly used in civil engineering, where they can be applied in façade structure. Traditionally used structural silicones are resistant to the external environment, but their low strength and elasticity do not meet the requirements of civil engineering. The greater spread of higher strength adhesives such as acrylates or polyurethanes is hampered by the lack of knowledge of their ageing resistance. The paper is focused on the experimental analysis of a double-lap shear joints of Silane Terminated Polymer (STP) adhesive applied in joints with aluminium and Zn-electroplated steel substrates with various surface treatments. The specimens were exposed to artificial ageing according to the technical regulations of the Timber Research and Development Institute in Prague. According to this regulation, specimens were exposed to changing of high and low temperatures, UV-radiation and humidity. This ageing should simulate 5 years in the climatic environment of Central Europe. Specimens exposed to laboratory ageing are compared with reference set of test specimens that were not artificially aged. STP demonstrated excellent resistance to laboratory ageing.

2019, Structures and Architecture: Bridging the Gap and Crossing Borders, Leiden, CRC Press/Balkema), p. 619-627), ISBN 978-1-138-03599-7

Current architecture offers many examples of glass load bearing structures such as panes, beams, balustrades, stairs or even columns. These members are mostly made of laminated safety glass panels. Individual plates in a laminated panel are bonded with a polymeric interlayer which has a significant influence on the shear forces transfer between them when the panel is perpendicularly loaded. This transfer meaningly depends on the interlayer´s shear stiffness. Even if this stiffness for a certain interlayer is available, the exact stress analysis of a laminated glass panel is rather difficult. This paper compares the results obtained by current analytical computational methods of double laminated perpendicularly loaded glass panel in various boundary conditions to the numerical simulation performed in RFEM 5®, shows marginal differences between these methods and gives further recommendations for a design of these structures in practice.

2019, The Journal of Adhesion, 95 (5-7), p. 632-652), ISSN 0021-8464

The effects of exposure to humid conditions in the extended cataplasm ageing test, based on ISO 9142, Procedure E2 on the mechanical properties of adhesively bonded joints, were investigated as a part of a comprehensive study on the ageing of an acrylate adhesive and a Silane-terminated polymer (STP) adhesive. The adhesives were applied in aluminium and Zn-electroplated steel substrates with various surface treatments (a smooth surface, a roughened surface, and anodized and blank aluminium) to observe the effect of ageing on joints with various substrates. The predominant effect of high relative humidity in the cataplasm test was compared with the results of immersion in water according to ETAG 002.

2019, IOP Conference Series: Materials Science and Engineering, Bristol, IOP Publishing Ltd.), ISSN 1757-899X

Many examples of glass load bearing structures such as beams, panes, balustrades, columns or even stairs can be found in a current architecture. These members are usually made of laminated glass panels. Glass plies of a laminated panel are bonded with polymeric interlayer significantly influencing shear forces transfer between them. It principally depends on a polymer shear stiffness which is affected by an ambient temperature and load duration. There is still general lack of knowledge regarding shear stiffness of most polymeric interlayers. Civil engineers thus design laminated glass members with excessive caution neglecting positive shear coupling of the glass plies provided by the interlayer. This approach leads to uneconomical and over-sized glass bearing structures profoundly preventing an extensive use of laminated glass in civil engineering. There are many polymer interlayers of different chemical composition available on the market. Mechanical properties of most of them are unfortunately not available for civil engineers dealing with laminated glass constructions design. This paper is focused on dynamic shear modulus of EVA (ethylene-vinyl acetate) and PVB (polyvinylbutyral) interlayer and their experimental investigation as a function of temperature and loading ratio. One possible way of determining this modulus is a shear dynamical thermal analysis (DMTA) which further enables to derive time and temperature dependent shear stiffness of EVA and PVB. This experimentally investigated property helps engineers design safer and cheaper glass constructions, possibly extending the use of laminated glass in a current architecture

2019, Book of abstracts of the 5th international conference on structural adhesive bonding AB2019, Porto, FEUP-Faculdade de Engenharia, Universidade do Porto), p. 142-142), ISBN 978-989-8927-74-3

The paper compares effects of three various ageing procedures (immersion according to ETAG 002, neutral salt spray test according to ISO 9142, Procedure E4, and extended cataplasm test based on ISO 9142, Procedure E2) among themselves on adhesives which are applicable in the civil engineering field. Research covers two different adhesives. Both adhesives were applied in double lap shear joints composed of aluminium and Zn-electroplated steel substrates with a roughened or smooth surface. Aluminium was used in two types of alloy and also as anodized aluminium due to its use in building facades. Chemical changes in the adhesive joint after ageing were investigated by FTIR analysis together with changes in mechanical properties and failure modes. Water absorption in adhesive was defined by immersion test according to ISO 62 to better understand changes in the adhesive joint after laboratory ageing.

2019, Advances and Trends in Engineering Sciences and Technologies III: Proceedings of the 3rd International Conference on Engineering Sciences and Technologies, Boca Raton, CRC Press), p. 89-95), ISBN 9780367075095

Looking at the current architecture, we may notice various examples of glass load bearing structures such as panels, beams, stairs or even columns. Most of these members are made of laminated safety glass with polymeric interlayer between the individual glass panes. Polymeric interlayer is able to provide the shear coupling of glass panes due to its shear stiffness, but this stiffness is temperature and load duration dependent. Therefore, the exact laminated glass panel analysis becomes difficult. This paper is focused on double laminated heat toughened glass panels in four-point bending tests. Panels are laminated with PVB interlayer and they are loaded in two different loading rates. In particular, normal stress distribution along the critical cross section and maximal vertical deflections depending on the loading rate are highlighted. Further, the comparison of the experimental data with simplified analytical calculation is elaborated. All bending tests were performed at CTU in Prague.

2019, Book of abstracts of the 5th international conference on structural adhesive bonding AB2019, Porto, FEUP-Faculdade de Engenharia, Universidade do Porto), p. 142-142), ISBN 978-989-8927-74-3

Adhesive bonding has a significant influence on the loadbearing and residual load-bearing capacity of the hybrid beam. Chosen adhesive has to ensure an adequate stiffness but on the other hand, it must be soft enough allowing a compensation of different temperature elongation of steel and glass and redistribution of stress peaks or other constraints.

2019, Sanace a rekonstrukce staveb 2019, Praha, České vysoké učení technické v Praze), p. 63-70), ISBN 978-80-02-02888-8

Vývoj lepidel pro konstrukční lepené spoje přináší nové možnosti jejich použití také ve stavebnictví, např. při kotvení fasádních panelů a spojování různých druhů materiálů, spojování ocelových prvků, v konstrukcích ze skla, ze dřeva, betonu, UHPC atd. Použití konstrukčních lepených spojů ve stavebnictví zahrnuje aplikace jak při rekonstrukcích, tak v novostavbách.

2019, Structures and Architecture: Bridging the Gap and Crossing Borders, Leiden, CRC Press/Balkema), p. 272-279), ISBN 978-1-138-03599-7

The paper is focused on the experimental analysis of double-lap shear joints of two-part acrylate and silane terminated polymer adhesives applied in joints with aluminium and Zn-electroplated steel substrates with various surface treatments. Residual mechanical properties and failure modes after laboratory ageing of specimens are compared with reference set of specimens, which was unexposed to ageing.

2019, International Journal of Mechanics and Materials in Design, 15 (1), p. 61-76), ISSN 1569-1713

Structural adhesive bonding is very often used joining method in aerospace and automotive industry, but in civil engineering, especially in façade applications, semi-flexible or semi-rigid adhesives are still rarely used. The article is focused on experimental analyses of structural adhesive joints intended for façade applications (e.g. bonding of façade cladding elements to the supporting substructure). The experimental study contains a comparison of the structural behavior of two different adhesives in joints with aluminum or zinc-electroplated steel substrates with various surface pre-treatments. The main goal of the study is a comparison of the mechanical properties of joints exposed and unexposed to laboratory ageing conditions; immersion on demineralized water according to ETAG 002 (Guideline for European Technical Approval for Structural Sealant Glazing Kits). Water content in adhesive layer can change significantly its mechanical properties and adhesion of glue to the substrate. Ageing resistance of joint can be improved by durability increasing of the substrate. For this reason, two different substrate materials with various surface treatments (mechanical roughening, smooth surface, anodizing) were tested. Different adhesive resistance against humid conditions was observed depending on the substrate material and pre-treatment. STP polymer joints showed strength reduction by 30% after immersion for almost all substrates, while acrylate adhesive proved 20% strength reduction for roughened aluminum substrate and 60% strength reduction for zinc-electroplated steel substrate with a roughened surface. The zinc-electroplated steel substrate showed problematic adhesion in case of the acrylate adhesive both reference set of specimens and specimens exposed to laboratory ageing. The positive effect of roughening on adhesion and ageing resistance was clearly observed in the specimens bonded by the acrylate adhesive.

2019, Journal of Building Engineering, 25, ISSN 2352-7102

As an outcome of the European COST Action TU1403 ‘Adaptive facades network’ - ‘Structural’ Task Group, this paper collects some recent examples and design concepts of adaptive systems, specifically including a new classification proposal and the definition of some possible metrics for their structural performance assessment. The aim is to provide a robust background and detailed state-of-the-art information for these novel structural systems, towards the development of standardized and reliable procedures for their mechanical and thermo-physical characterization.

2019, Journal of Building Engineering, 25, ISSN 2352-7102

In this paper, existing fundamental standards for testing traditional facades are first recalled and commented. Special care is spent for the validity and reliability of conventional testing methods for innovative, adaptive envelopes, including a discussion on selected experimental methods for facade components and systems. Nonconventional testing procedures which may be useful for adaptive skins are then also discussed in the paper, as resulting from the research efforts of the European COST Action TU1403‘Adaptive facades network’ - ‘Structural’ Task Group.

2019, Rehabilitation and Reconstruction of Buildings II, Curich, Trans Tech Publications), p. 115-122), ISBN 978-3-0357-1492-0, ISSN 1013-9826

Laminated glass is a structural element used extensively in a reconstruction of existing building structures because of its transparency and simplicity. When using laminated glass as a glass staircase, balustrades, transparent flooring, facades or other structural elements, it is advisable to consider the shear interaction of individual glass panes in the cross-section. A conservative approach where the glass panes shear interaction is not considered, is uneconomical. This interaction depends on the properties of polymeric interlayers used in lamination process. Various commercial products based on PVB (polyvinyl butyral), EVA (ethylene vinyl acetate), ionomer, or thermoplastic polyurethane (TPU) are used. Stiffness of polymers depends on temperature and duration of a load. Interlayers exhibit the viscoelastic properties and temperature dependency usually described by the generalized Maxwell model and WLF model (Williams-Landel-Ferry). Parameters of these models are the most effectively determined by Dynamic Mechanical Thermal Analysis (DMTA), where the material is cyclically loaded at different frequencies and temperatures. Material parameters were found by DMTA in shear for PVB type of interlayer Trosifol® BG R20. In addition, the experimental quasi-static loading tests in shear were performed at different loading rates and at various temperatures. These experimental stress-strain diagrams were compared to the theoretical stress-strain relations obtained from Maxwell model with material parameters based on DMTA testing. All tests were performed in Klokner Institute CTU in Prague.

2018, Facade 2018 - adaptive!, Delft, TU Delft), p. 175-179), ISBN 978-94-6366-102-7

Building façade is a very specific type of usage for adhesive connections due to the requirements for durability, strict geometrical imperfections and joining of unconventional materials often used in the façade design. At the same time, an adhesive joining by semi-flexible and semi-rigid adhesives is still relatively new bonding method in facade applications in comparison with usage in aerospace and automotive industry. For that reason, extensive experimental study was performed to assess residual shear strength of adhesives exposed to three various ageing procedures.

2018, Proceedings of the 12th International fib PhD Symposium in Civil Engineering, Praha, ČVUT v Praze, Fakulta stavební), p. 265-271), ISBN 978-80-01-06401-6

This paper focuses on a description of an interaction of glass and cement-composite material UHPC (Ultra Hight Performance Concrete) when applied to a footbridge construction. If we know, the application of the connection between the glass and the UHPC has not been investigated for the structure of the footbridge. The use of UHPC material improves static properties of these structures, allows them to extend their servis life, saves materials and reduces maintenance costs. The UHPC has a high resistence to environmental influences. Glass is characterized by a combination of high stiffness and compressive strength with a relatively low density. In terms of these properties, glass is suitable for the production of lightweight structures with high strength and durability. The proposed footbridge is a new opportunity to make effective use of the properties of both materials. The paper translates a development of the design system and it's testing on numerical models together with possibilities of solving a detail of the glass-UHPC connection.

2018, Book of Abstracts of 12th European Adhesion Conference and 4th Luse-Brazilian Conference on Adhesion and Adhesives, Publindústria, Produção de Comunicação, Lda.), p. 155-157), ISBN 978-989-8927-24-8

2018, INTRO, 2018 (6), p. 18-21), ISSN 2570-7744

Článek pojednává o historii skla ve stavebnictví, o materiálových vlastnostech, o různých typech skla pro stavebnictví, včetně vrstveného. Vysvětluje vliv použitého polymerního materiálu na vlastnosti vrstveného skla. Popisuje praktické problémy použití skla na fasádách budov, např. stárnutí a vliv okolního prostředí. v závěru se článek věnuje konkrétním příkladům užití skla na fasádách.

2018, International Journal of Adhesion and Adhesives, 83, p. 168-177), ISSN 0143-7496

Contemporary architecture often requires adhesive connections as a bonding method of façade cladding elements to the supporting substructure, due to their visually smooth surface without the interruption by bolts. Low strength, elastic and durable silicone sealants have been used in façades for a long period of time, but there is a lack of information about semi-flexible and semi-rigid adhesives with higher strengths. The building façade is a very specific application for adhesive connections due to the requirements for durability, strict geometrical imperfections and joining of unconventional materials often used in the façade design. The presented paper is focused on experimental analyses of structural adhesive joints exposed to laboratory aging conditions. Due to the absence of a particular code intended for structural adhesive joints in façades, two artificial aging procedures were chosen – ETAG 002 and ISO 9142 - E4 Procedure (Exposure to neutral salt spray and elevated temperature and humidity). The joints are bonded by two different adhesives, Silane Terminated Polymer (STP), and a two-part acrylate adhesive. The joints are composed of blank aluminum with a smooth and roughened surface, anodized aluminum and galvanized steel with a smooth and roughened surface. Mechanical behavior and failure modes of a reference set of specimens are compared with the results of two specimen sets exposed to aging. The degrading effect of demineralized water immersion was more crucial for the STP adhesive than the salt spray test. On the contrary, the effect of the salt spray test was more serious for the acrylate adhesive than immersion in water. The experimental study showed that the degrading effect of a particular aging procedure can be more harmful to one adhesive than the others in dependence on the time of exposure.

2018, ESaT 2018, Košice, Technická univerzita v Košiciach, Stavebná fakulta), ISBN 978-80-553-2982-6

There are various examples of glass load bearing structures such as beams, panels, columns or even stairs in a current architecture. These members are mostly made of laminated safety glass with a polymeric interlayer between the individual glass panes. The interlayer is able to provide shear coupling of the glass panes in bending due to its shear stiffness, but this stiffness is temperature and load duration dependent. Therefore, the exact laminated glass panel analysis becomes difficult. This paper is focused on double laminated heat toughened glass panels in four-point bending tests laminated with PVB interlayer loaded in two different loading rates. In particular normal stress distribution along the critical cross section depending on the loading rate, maximal vertical deflections and comparison of the experimental data with simplified analytical calculation are elaborated. All bending tests were performed at CTU in Prague.

2018, Koroze a ochrana materiálu, 62 (2), p. 54-64), ISSN 1804-1213

Tento článek byl zaměřen na vyhodnocení vlivu expozice neutrální solné mlhy (dle ISO 9124), postupem E4, na mechanické vlastnosti nosných lepených spojů. Studie také posuzuje vliv podkladu lepeného spoje (ocel, slitiny hliníku) a jeho povrchové úpravy (galvanické zinkování, eloxování) a stupně zdrsnění (ověřeno prostřednictvím optické konfokální mikroskopie) na mechanické vlastnosti spoje. Experimentální program zahrnoval lepidla na bázi akrylátu a na kombinované bázi silikonu a polyuretanu, která byla aplikována v dvojitě přeplátovaných spojích zatěžovaných smykem.

2018, International Journal of Structural Glass and Advanced Materials Research, ISSN 2616-4515

Adaptive facades are getting more and more widespread in modern buildings. These facade systems, among many others, need to fulfil the requirements of several structural considerations, such as structural safety, serviceability, durability, robustness and fire safety, being typically defined for standard facades and building enclosures in general. The current paper discusses special structural characteristics which need to be taken into account when designing adaptive facades and summarizes some recent efforts of the activities in progress carried out by the ‘Structural’ Task Group (TG2.4) of the European COST Action TU1403 ‘Adaptive Facades Network’.

2018, Challenging Glass 6 - International Conference on the Architectural and Structural Application of Glass, Delft, TU Delft), p. 417-426), ISBN 978-94-6366-044-0

This paper is focused on the shear modulus of PVB (polyvinyl-buthyral) and SentryGlas (ionoplast) experimental investigations as a function of temperature and loading ratio. It is possible to find out these functions by static creep or relaxation tests as well as by dynamic mechanical thermal analysis-DMTA. A lot of DMTA experiments in shear with the aforementioned interlayers in various loading conditions have been performed in order to determine their shear stiffness. It also enables to identify their Prony parameters as a part of the next survey.

2018, Challenging Glass 6 - International Conference on the Architectural and Structural Application of Glass, Delft, TU Delft), p. 309-320), ISBN 978-94-6366-044-0

This paper reports on a Finite Element numerical investigation carried out on small-scale adhesive joint specimens. Taking advantage of a past experimental study performed at CTU in Prague - focused on both material tests and small-scale adhesive connections subjected to shear loading - the numerical modelling approach is validated by taking into account a selection of shear tests on glass-to-steel adhesive joints. The typical specimen is composed of two glass plates bonded to two steel plates with a gap between them and four adhesive joints per one specimens. Finite Element numerical analyses are presented, as obtained from full 3D solid models representative of the specimens components.

2018, TZB info, 20 (30.04.2018), ISSN 1801-4399

V současné architektuře se můžeme setkat s mnoha typy nosných konstrukcí ze skla, jako jsou nosníky, desky, schodiště nebo sloupy. Většina těchto prvků je vyrobena z vrstveného skla. Jednotlivé skleněné desky v souvrství jsou spojeny polymerní folií a přenos smykových sil mezi těmito deskami je předmětem současného výzkumu. Tento článek je zaměřen na experimentální stanovení počátečního smykového modulu folií PVB (Trosifol BG-R-20, Trosifol Extra Strong) a EVA (Evasafe) v závislosti na teplotě a rychlosti zatížení, porovnání tuhostí těchto folií a shrnutí důležitých výsledků.

2018, TZB-info: portál pro technická zařízení budov, 20 (10.09.2018), ISSN 1801-4399

Ohýbané nosné konstrukce z vrstveného skla jsou v dnešním stavitelství navrhovány stále častěji, a to především kvůli své zbytkové únosnosti v nehodové situaci. Tento článek je zaměřen na výpočet napjatosti a průhybů ohýbané po obvodě prostě podepřené čtvercové desky z vrstveného skla zatížené rovnoměrným krátkodobým zatížením, který zohledňuje experimentálně stanovenou smykovou tuhost běžných polymerních folií PVB (Trosifol BG-R-20, Trosifol ExtraStrong) a EVA (Evasafe).

2018, Proceeding of PLACES AND TECHNOLOGIES 2018, University of Belgrad), p. 493-499), ISBN 978-86-7924-199-3

Adaptive facade systems are getting increasingly common in modern buildings envelopes. Their adaptive behaviour poses special requirements concerning structural aspects of the façade. In the present paper, an overview of the possible classification of structurally adaptive facades and related requirements is given. Furthermore, it is discussed how changes in their structural characteristics needs to be properly taken into account when testing and modelling their performance. The main challenges of the aforementioned aspects are hencebriefly highlighted in the paper.

2018, Building Performance Simulation and Characterization of Adaptive Facades – Adaptive Facade Network, Delft, Delft University of Technology (TU Delft)), p. 166-177), ISBN 978-94-6366-111-9

improve energy and thus cost, efficiency of both new and refurbished buildings by responding to the changes in the outdoor conditions. Furthermore, they can provide healthy and comfortable indoor environment to the building occupants, by adjusting the response to their needs.

2018, Facade 2018 - adaptive!, Delft, TU Delft), p. 325-336), ISBN 978-94-6366-102-7

Adaptive facades are getting more and more widespread in modern buildings. These facade systems, among many others, need to fulfil the requirements of several structural considerations, such as structural safety, serviceability, durability, robustness and fire safety, being typically defined for standard facades and building enclosures in general. The paper discusses special structural characteristics which need to be taken into account when designing adaptive facades, and summarizes some recent efforts of the activities carried out by the ‘Structural’ Task Group (TG2.4) within the European COST Action TU1403 ‘Adaptive Facades Network’.

2017, International Journal of Adhesion and Adhesives, 72, p. 10-22), ISSN 0143-7496

This paper reports on an investigation of glued joints in glass load-bearing structures, with reference to the effect of various substrates (glass, steel, stainless steel, aluminium) and their surface treatment (sandblasting for the glass surface) on the adhesion of selected adhesives. The thickness of the adhesive layer and the effect of artificial ageing - a simulation of 5 years of ageing in outdoor central-European conditions - are also discussed. Tensile and shear tests were carried out on three series of specimens with various adhesives and substrates - two series for tensile and shear tests, and one series for shear tests on specimens exposed to ageing. Our results show that sandblasting the glass surface can improve the adhesion, and thus the strength values, of an adhesive joint in cases where, with a smooth glass surface, cohesive failure is not reached. The thickness of the adhesive layer had a significant effect for a semi-rigid acrylate adhesive, where the joint achieved higher strength values with less thickness of the glue. The effect of ageing varied according to the adhesive. The most visible changes were observed for a two-component acrylate adhesive and for methacrylate UV-adhesives. One of the selected glues was marked as unsuitable for load-bearing connections due to significant worsening of its mechanical properties after ageing.

2017, Advances and Trends in Engineering Sciences and Technologies II: Proceedings of the 2nd International Conference on Engineering Sciences and Technologies, Boca Raton, CRC Press), p. 187-192), ISBN 978-1-138-03224-8

Adhesive connections offer a number of benefits in structural applications, especially in the case of brittle adherends such as glass. This paper reports on an experimental anal-ysis aimed at determining the mechanical characteristics of the two types of the same acrylate adhesive product (a new technology adhesive and its predecessor), both produced by the same manufacturer. The adhesive connections were applied in planar connections under shear loading. Finite element analysis shows that it is necessary to use different material models for the two types of adhesive, due to their completely different mechanical properties and behavior un-der loading. The numerical analysis deals with the application of various material models used for modelling the old and the new types of acrylate adhesives, and provides a comparison of numerical and experimental results.

2017, IOP Conference Series: Materials Science and Engineering, Bristol, IOP Publishing Ltd), ISSN 1757-899X

Noticing the current architecture, there are many examples of glass bearing members such as beams, panes, ribs stairs or even columns. Most of these elements are made of laminated glass from panes bonded by polymer interlayer so the task of transferring shear forces between the glass panes needs to be investigated due to the lack of knowledge. This transfer depends on stiffness of polymer material, which is affected by temperature and load duration. It is essential to catch the safe side with limit cases when designing these members if the exact material behaviour is not specified. There are lots of interlayers for structural laminated glass applications available on a market. Most of them exhibit different properties, which need to be experimentally verified. This paper is focused on tangent shear modulus of PVB (polyvinyl-buthyral) interlayer and its effect on the stress distribution in glass panes when loaded. This distribution may be determined experimentally or numerically, respectively. This enables to design structural laminated glass members more effectively regarding price and safety. Furthermore, this is the way, how to extend the use of laminated glass in architectural design.

2017, Progress in Mechanics and Materials in Design, Porto, Edicoes INEGI), p. 115-116), ISBN 978-989-98832-6-0

An extended abstract is focused on structural adhesive joints exposed to artificial ageing by immersion in demineralized warm water. Experimental analysis and results showed a significant deterioration of mechanical properties for acrylate adhesive while silane terminated polymer showed slight worsening only.

2017, Proceedings of the 7th International Conference on Mechanics and Materials in Design, Porto, Edicoes INEGI), p. 325-332), ISBN 978-989-98832-7-7

The article is focused on experimental analyses of structural adhesive joints intended for façade applications (e.g. bonding of façade cladding elements to the supporting substructure). The experimental study contains a comparison of the structural behavior of two different adhesives in joints with aluminum or galvanized steel substrates with various surface pretreatments. It also compares the mechanical properties of joints exposed and unexposed to laboratory ageing conditions according to ETAG 002 (Guideline for European Technical Approval for Structural Sealant Glazing Kits).

2017, Ne-xt facades, Technical University of Munich), p. 98-99), ISBN 978-94-6366-105-8

Modern building envelopes are high-tech components that must meet requirements and constraints regarding architecture/urban planning/aesthetics, energy efficiency, indoor environmental quality, buildability and value. If a facade can respond to all the transient conditions while maintaining occupant satisfaction without imposing additional loads on the building services, it can be considered “fully adaptive”. However, an adaptive facade needs to fulfil a fundamental role as assigned to the structural performance of the same assemblies, under ordinary as well as exceptional loads, hence requiring specific safety levels and design concepts. Most of the systems representative of this next generation of facades typically consist of highly adaptive envelopes, generally involving smart materials, kinematic mechanisms, etc. In this regard, the current lack of standardized procedures to evaluate and test the structural performance of adaptive envelopes and components represents the first barrier towards their widespread adoption. This is especially true in the case of strategic buildings, in which the facade could be exposed to exceptional loading conditions or the building envelop could have a significant contribution to the robustness of the entire structural system. Similarly, there currently are no guidelines and recommendations for the numerical modelling of the mechanical performance of adaptive facades. In this context, the activities carried out by the EU COST Action TU1403 “Structural Task” aims to provide a proposal of classification for novel structural skins considering their structural properties and expected performances. The Structural Task program will provide an overview of important experimental facilities available in Europe for testing the static, dynamic, long-term and fire performances of adaptive systems.

2017, Ne-xt facades, Technical University of Munich), p. 96-97), ISBN 978-94-6366-105-8

In contrast to other joining methods, such as bolting or riveting, adhesive bonding has no unfavourable effect on the parts to be connected. There are no interruptions by holes which create stress concentrations and disrupt visually smooth and flat surface of joining parts. An important benefit of glued connections in facades is an elimination of local thermal bridge in comparison with bolted connections. For these reasons, gluing is a very useful bonding method for façade applications. Low strength, elastic and durable silicone sealants are applied in facades for a long period of time, but there is a lack of information about semi-flexible and semi-rigid adhesives with higher strengths. In the development of adhesively bonded joints for facades, long-term durability is an important area of attention.

2017, Book of abstracts of the 4th international conference on structural adhesive bonding AB 2017, Publindústria, Produção de Comunicação, Lda.), ISBN 978-989-723-243-5

Paper is focused on the experimental results of adhesive joints exposed to artificial ageing procedures - ETAG 002 and ISO 9142 - Procedure E4 (Exposure to neutral salt spray and elevated temperature and humidity).

2017, Structural and Mechanical Engineering for Security and Prevention, Curich, Trans Tech Publications), p. 279-285), ISBN 978-3-0357-1236-0, ISSN 1013-9826

A lot of different polymeric interlayers with different properties are available on a market but their experimentally determined material properties with respect to the load duration and temperature are not mostly specified. Structural engineers tend to design laminated glass structural elements on the safe side and do not take the interlayer stiffness into account. This paper is focused on two types of PVB (polyvinyl-buthyral interlayers) experimental investigation under various temperature and loading rate conditions.

2017, Eurosteel 2017, Berlin, Ernst & Sohn), p. 679-684), ISSN 2509-7075

This paper reports on an experimental analysis focused on determining of the mechanical characteristics of two types of adhesive applied in double lap connection loaded by shear. The study comprises two basic substrate materials, aluminium and galvanised steel, with various surface treatments.